Ionosphere delay measurement using carrier phase

Abstract

One or more atmospheric propagation effects are estimated by using a phase comparison between and upper sideband and a lower sideband of a modulated signal. In one embodiment, one or more propagation effects are estimated by using a phase comparison between an upper sideband and a lower sideband of a satellite navigation signal. In one embodiment, one or more ionospheric propagation effects are estimated by using a phase comparison between an upper sideband and a lower sideband of a GPS M-code signal.

Description

BACKGROUND [0001] 1. Field of the Invention [0002] The present invention relates to measurement of ionospheric propagation effects on Radio Frequency (RF) signals by comparing carrier phase between signals of different frequency, such as, for example, upper and lower sidebands of a GPS M-code signal. [0003] 2. Description of the Related Art [0004] In the upper regions of the earth's atmosphere, ultraviolet and X-ray radiation coming from the sun interact with the atmospheric gas molecules and atoms. These interactions result in ionization giving rise to large numbers of free “negatively charged” electrons and “positively charged” atoms and molecules. The region of the atmosphere where gas ionization takes place is called the ionosphere. It extends from an altitude of approximately 50 km to about 1,000 km or higher (the upper limit of the ionospheric region is not clearly defined). [0005] The electron density within the ionosphere is not constant. It changes with time and altitude. T...

AI Technical Summary

Benefits of technology

The patent describes a system that uses a phase comparison between an upper sideband and a lower sideband of a multi-carrier modulated signal to estimate the propagation effects of a dispersive medium, such as the ionosphere. This system can provide improved quality, redundancy, resistance to spoofing, and resistance to jamming by making separate ionospheric measurements by comparing signals transmitted using carriers in different frequency bands. The system can also use the relative phase measurement to verify the authenticity of a received signal and to assist in resolving phase ambiguity. Additionally, the system can monitor relatively short-term ionospheric TEC levels and can correct the phase to recover the modulation data.

Problems solved by technology

In the case of satellite navigation systems, such as, for example, the Global Positioning System (GPS), bending of the signal propagation path causes a relatively small range error, particularly if the satellite elevation angle is greater than 50 degrees.

However, the change in the propagation speed causes a significant range error, and therefore should be accounted for.

As the ionosphere is a dispersive medium, it causes a delay that is frequency dependent.

Single frequency band receivers cannot take advantage of the dispersive nature of the ionosphere.

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